Data communication systems based on fiber optics provide substantially higher bandwidth than systems based on electrical systems. Unfortunately, switching devices for switching optical signals between an input fiber and a plurality of output fibers have not kept pace. As a result, optical signals are typically converted back to electrical signals prior to switching. The electrical signals are then switched using conventional packet switching techniques and reconverted to optical signals prior to entering the output fibers. The limitations of electrical switching systems prevent the realization of the full data bandwidth of the fibers. Accordingly, a significant amount of research has gone into developing optical switches that avoid the conversion of the light signals back to electrical signals.
One promising method for switching optical signals between optical paths relies on a waveguide whose location is electrically controlled. A waveguide may be generated by altering the index of refraction of a medium along the path over which the light is to travel such that the desired path has a higher index of refraction than the surrounding medium. Devices based on liquid crystals are particularly attractive because of the large changes in index of refraction that can be induced in a liquid crystal layer by applying a low frequency AC electrical field across the layer. A simple switching device can be constructed by energizing one set of electrodes on the surface of the liquid crystal layer while leaving an alternative set in a non-energized state. The region between the energized electrodes then becomes the waveguide that specifies the direction in which the light signal will propagate in the liquid crystal layer.
Unfortunately, liquid crystal based light guides only guide light of one linear polarization. Light of the orthogonal polarization experiences a different index of refraction and is not guided. Since optical signals in such systems typically have randomly changing polarization states, unpredictable transmission can occur.
Broadly, it is the object of the present invention to provide an improved optical switching element.
It is a further object of the present invention to provide an optical switching element that operates on a light signal independent of the polarization state of that light signal without introducing the light losses inherent in polarization dependent waveguides.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.